This invention relates to an apparatus for mounting a drill on a pipe, and in particular to an apparatus adapted to cope with pipes of large diameter.
One known method of holding a drill steadily against a pipe is using a magnetic system. This would include, for example, an electromagnetic holder, which when energised, holds a drill firmly against a metallic pipe, so that a hole may be drilled in a defined position in the pipe. However, a magnetic holder suffers from several major problems. It cannot be used with pipes made from a non-magnetic material, such as concrete, plastic, stainless steel, brass or clay. It cannot be used in environments which are particularly sensitive to electrical or magnetic fields, such as radar installations or computer factories. A separate safety chain has to be used as well, because in the event of a power failure to the electromagnetic clamp, care needs to be taken to ensure that the entire apparatus does not fall and injure operators who may be standing nearby. Also, magnetic mountings cannot withstand large forces without being becoming dislodged.
WO98/16353 discloses an apparatus for mounting a drill onto a pipe, in which a frame is clamped onto the pipe, and a drill press is adjustably mounted on the platform. The drill press stand can be adjusted relative to the platform, in a direction parallel to the axis of the pipe to be drilled, and the pipe may be drilled radially. By allowing the drill press stand to be adjusted relative to the platform, a more flexible arrangement is possible. One embodiment involves using a clamp which fits around the pipe, constructed from a front plate and a back plate held together by a series of screws. In a second embodiment, the clamping means is an inverted V-shape frame which sits on top of the pipe, and is connected at both sides to a chain which loops around the pipe. The chain can be tightened against the frame to fix the clamp in position. This is done by means of adjustable tension units which are fixed to the frame, and have chain holding hooks. The hooks can be raised or lowered relative to the frame, to tighten or loosen the chain.
The frame with the chain in WO98/16353 is more suitable than a simple rigid clamp for use in restricted space, due to the flexibility and relatively small volume of the chain. However, it is not readily suited for drilling into pipes of very large diameter. One problem is that the tension units pull the chain tight in a direction perpendicular to the platform. This works well for small pipes where the diameter of the pipe is not much larger than the width of the platform. However, for large pipes with diameter much larger than the width of the platform, the part of the chain which attaches to the tension units lies almost parallel to the surface of the pipe. Thus when the hook in the tension unit is raised to tighten the chain, it mainly has the effect of lifting up the end of the chain, rather than tightening it, and the amount by which the chain can be tightened is very small.
A second problem is that for large pipes, only a small part of the circumference of the pipe is encompassed within the inverted V shape of the platform. The platform is therefore likely to slip or become dislodged after it has been positioned. The chain would be unlikely to clamp tightly enough with such an arrangement, which would be a particular problem for a large pipe made from a hard material, such as a steel pipe of 70 cm diameter or more which had to have large holes drilled in situ. The chain might jump off the hook during drilling.
Although these problems might be eliminated by simply scaling the whole clamp to a very much larger size, the apparatus would then be unsuitable for smaller pipes, and extremely unwieldy.
Aspects of the invention are set forth in the accompanying independent claims and preferred features are set forth in the dependent claims.